Rock-physics modeling wave dispersion and attenuation signatures of multiscale fractured rocks

Fractures in the subsurface, spanning scales from microscopic cracks to macroscopic faults, significantly influence the mechanical, hydraulic, and seismic properties of rock systems. Understanding and modeling the influences of multiscale fractures on the seismic wave dispersion and attenuation plays a critical role in advancing geophysical exploration, enhancing reservoir characterization, and improving the predictive capabilities for energy resource management and geohazard assessment. However, existing theoretical models often address the wave dispersion and attenuation for the single-scale fractures, lacking a unified framework to integrate multiscale and multiphysical processes. We develop a unified theoretical model that comprehensively characterizes seismic wave dispersion and attenuation in multiscale fractured rocks. The model integrates mechanisms such as microscale squirt flow, mesoscopic fluid flow between fractures and background pores, fluid flow between intersecting fractures, and scattering attenuation, while accounting for fracture lengths spanning five orders of magnitude (from 10−4 to 101 m), as well as their orientation, filling materials, and distribution patterns. Multiscale fractured rocks exhibit pronounced scale-dependent elastic properties, characterized by decreasing velocity and increasing attenuation with increasing scale. Mesoscopic fluid flow between fractures and background pores, as well as fluid flow between intersecting fractures, is the dominant mechanisms of seismic wave attenuation in earthquake and exploration seismic frequency bands, while scattering attenuation plays a critical role under gas-saturated conditions. In fractal distributions, these effects become particularly significant at seismic scales, whereas in log-Gaussian distributions, the most notable changes occur at the logging scale. The developed modeling framework has the potential to improve the understanding and predictive capabilities of fracture-dominated systems and enhance the interpretation of multiscale fractures using cross-scale geophysical data.